Medical ventilators may determine when a patient takes a breath in order to synchronize the operation of the ventilator with the natural breathing of the patient. In some instances, detection of the onset of inhalation and/or exhalation may be used to trigger one or more actions on the part of the ventilator.
The response performance of a medical ventilator to a patient trigger from the exhalation breath phase into inhalation is an important characteristic of a medical ventilator. A ventilator's trigger response impacts the patient's work of breathing and the overall patient-ventilator synchrony. In patient-initiated ventilation types such as Pressure Support Ventilation (PSV), Proportional Assist Ventilation PAV), etc., the airway pressure drops below the baseline as a patient initiates an inspiratory effort. The ventilator detects the patient's inspiratory effort and uses this information to provide ventilation therapy to the patient.
The trigger response performance of a ventilator is a function of a patient's inspiratory behavior (which includes breathing effort magnitude and timing characteristics) as well as the ventilator's gas delivery dynamics and flow control parameters (actuator response, deadbands, etc.). In conventional pressure triggering modality, the patient effort is detected based on the magnitude of airway pressure drop from the operator-set positive end-expiratory pressure (PEEP). The pressure drop is generated by the patient inspiratory effort as sensed at a patient proximal site in the gas delivery system with no or minimal base flow. The pressure trigger sensitivity is used to determine a phase transition from exhalation into inhalation. In the presence of system leaks, there is a need to provide an adequate base flow to compensate for the leak rate and avoid autocycling (false breath triggering) due to airway pressure drop exceeding the set sensitivity in the absence of patient inspiratory effort.